I can’t see anyone putting checking account money into a gold backed crypto, first because you have to pay transaction fees to convert fiat to gold crypto (which you don’t if you just keep it as fiat) and second as you note, every “spend” is a capital gain tax event (and few countries exempt capital gains). It does become an accounting nightmare to work out the gains and in Australia at least, concessional tax rates on capital gains only apply if you hold the asset for 1 year or more, so many of the “spends” could end up being taxed at ordinary income rates.
As to the stablecoin opportunity, that is a possibility and it would generate more buy/sell volumes as the crypto bros trade in and out more frequently than your average gold investor, but they won’t use it for spending either. At the moment that market has few competitors (http://vaultoro.com, https://www.bitpanda.com/en/metals, https://digix.global/ for example) so there is an opportunity but success here requires connections and marketing into the crypto community. Vaultoro has the lead in this space IMO having been around since 2015 but Kinesis has been active. The other one to watch is https://www.paxos.com/ which is a US regulated USD stablecoin but which was reportedly looking at doing a gold stablecoin.
Re “The rules no longer apply” I wouldn’t be so sure. Certainly according to FinCEN https://www.fincen.gov/sites/default/files/2019-05/FinCEN%20Guidance%20CVC%20FINAL%20508.pdf Kinesis type systems are money transmission services so those regulations apply.